Multilayer type printed-wiring board and method of measuring impedance of multilayer type printed-wiring board

ABSTRACT

The impedance of a newly manufactured data transmission wire pattern can be measured easily and accurately. A multilayer type printed-wiring board  1  comprises a pair of data transmission wire patterns  4, 5  arranged between a CPU module  2  and a memory module  3  on respective inner layer substrates  6, 7,  impedance measuring wire patterns  21  and  22  arranged respectively in the layers same as those of the data transmission wire patterns  4, 5,  a prepreg layer  11  arranged on the impedance measuring wire patterns  21, 22,  land sections  23, 23  for signals arranged on the prepreg layer  11  and electrically connected to the impedance measuring wire patterns  21, 22  so as to be brought into contact with the signal terminal  41  of a probe  40  and a GND land section  24  also arranged on the prepreg layer  11  and electrically connected to the impedance measuring wire patterns  21, 22  so as to be brought into contact with the GND terminal  42  of the probe  40,  the impedance measuring wire patterns  21, 22  having a pattern length not smaller than 30 mm that is the minimal length required for use with a TDR unit and a pattern width same as that of the data transmission wire patterns  4, 5.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a multilayer type printed-wiring boardprovided with a checking coupon for measuring the characteristicimpedance of the data transmission wire pattern arranged between a CPUmodule and a memory module.

2. Related Background Art

Electronic devices such as game machines for home use and mobiletelephone sets typically comprises a printed-wiring board arranged inthe cabinet thereof and a CPU (central processing unit) module and amain memory module are mounted there along with other modules. The CPUmodule and the memory module are connected to each other by a datatransmission wire pattern arranged on the printed-wiring board.

Meanwhile, the data transmission wire pattern of a printed-wiring boardhave to be designed in such a way that the impedance of the wire patternshows a value that corresponds to the impedance specified for the CPUmodule and the memory module mounted on the printed-wiring board so thatthe CPU and the memory may operate reliably on a stable basis.

However, some of the data transmission wire patterns of theprinted-wiring boards shipped from manufacturing plants after thecompletion of the manufacturing process can show discrepancies betweenthe design values and the actual values due to various reasons includingthe conditions for etching copper foils in the data transmission wirepatterns to consequently give rise to an impedance greater or smallerthan the design value. When the impedance does not agree with the designvalue, it is no longer possible to transmit exchange signals between theCPU module and the memory module.

BRIEF SUMMARY OF THE INVENTION

In view of the above circumstances, it is therefore an object of thepresent invention to provide a novel multilayer type printed-wiringboard adapted to measuring the impedance of the data transmission wirepattern on the manufacturing floor in an easy and simple fashion.

Another object of the present invention is to provide a multilayer typeprinted-wiring board comprising a pair of data transmission wirepatterns arranged at the opposite sides of the inner layer substrate andadapted to measuring the impedances of the two data transmission wirepatterns in a single measuring operation to improve the efficiency ofthe measurement process.

According to the invention, the above objects are achieved by providinga multilayer type printed-wiring board comprising;

a first insulating layer;

a data transmission wire pattern arranged on said first insulating layerand adapted to data transmission between a CPU module and a main memorymodule to be used for the CPU;

an impedance measuring wire pattern arranged on said first insulatinglayer in the layer same as that of said data transmission wire patternwith a predetermined clearance to any adjacent wiring pattern;

a second insulating layer arranged on said data transmission wirepattern and said impedance measuring wire pattern; and

land sections for signals arranged on said second insulating layer andelectrically connected to said impedance measuring wire pattern arrangedon said first insulating layer by way of a through hole so as to be heldin contact with the signal terminal of the probe for measuring theimpedance of said impedance measuring wire pattern and a GND (grounding)land section held in contact with the GND terminal of said probe;

said impedance measuring wire pattern having a pattern length notsmaller than about 30 mm and a pattern width same as that of said datatransmission wire pattern when using a TDR (time domain reflectometer)unit.

As pointed out above, the impedance measuring wire pattern for measuringthe impedance of the multilayer type printed-wiring board is arranged inthe layer same as that of the data transmission wire pattern adapted todata transmission between the CPU module and the main memory module tobe used for the CPU, for which a certain level of impedance have to besecured.

Preferably, the transmission frequency of said data transmission wirepattern of said multilayer type printed-wiring board is not less than130 MHz so as to allow high speed data transmissions.

Preferably, the clearance between said impedance measuring wire patternof said multilayer type printed-wiring board and any adjacent wiringpattern is not less that twice of the pattern width of said impedancemeasuring wire pattern so as not to have any interference of theadjacent wiring pattern.

Preferably, the wiring pattern arranged around the impedance measuringwire pattern of the multilayer type printed-wiring board is a GNDpattern connected to said GND land section by way of a plurality ofthrough holes so as to eliminate any inductance component.

Still preferably, when a plurality of data transmission wire patternsare arranged in different layers in said multilayer type printed-wiringboard, a plurality of impedance measuring wire patterns are arranged indifferent layers in correspondence to the respective data transmissionwire patterns and electrically connected to each other by way of throughholes.

Thus, with a multilayer type printed-wiring board according to theinvention, since an impedance measuring wire pattern is arranged in thelayer of the data transmission wire pattern and the pattern width thataffects the impedance of the device is made equal to that of the datatransmission wire pattern so that the impedance of the data transmissionwire pattern can be measured accurately by means of a method ofmeasuring the impedance of a multilayer type printed-wiring boardaccording to the invention. The impedance of a multilayer typeprinted-wiring board can be measured accurately by means of a TDR (timedomain reflectometer) unit when the impedance measuring wire pattern hasa pattern length not smaller than about 30 mm.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

FIG. 1 is a schematic plan view of an embodiment of multilayer typeprinted-wiring board according to the invention;

FIG. 2 is a schematic cross sectional view of a principal part of themultilayer type printed-wiring board of FIG. 1;

FIG. 3 is an exploded schematic perspective view of a checking patternarranged on the multilayer type printed-wiring board of FIG. 1;

FIG. 4A is a schematic plan view of the checking pattern of FIG. 3 andFIG. 4B is a schematic cross sectional view of the checking pattern ofFIG. 3.

FIG. 5 is a schematic perspective view of a principal part of themultilayer type printed-wiring board of FIG. 1 being measured forimpedance by means of a TDR unit;

FIG. 6 is a graph illustrating the waveform of the impedance of themultilayer type printed-wiring board of FIG. 1; and

FIG. 7 is a schematic cross sectional view of another embodiment ofmultilayer type printed-wiring board according to the invention.

DETAILED DESCRIPTION OF THE INVENTION

Now, a multilayer type printed-wiring board and a method of measuringthe impedance of a multilayer type printed-wiring board according to theinvention will be described in greater detail by referring to theaccompanying drawing. FIG. 1 is a schematic plan view of an embodimentof multilayer type printed-wiring board according to the invention. Themultilayer type printed-wiring board 1 has a total of sixelectro-conductive layers and is adapted to be used in a game machinefor home use.

Referring to FIG. 1, the multilayer type printed-wiring board 1comprises a CPU (central processing unit) module 2 and a pair of memorymodules 3, 3 to be used for the CPU module 2 that are arranged on one ofthe opposite sides of the multilayer type printed-wiring board 1. TheCPU module 2 has an operating frequency higher than that of any ordinaryCPU and is adapted to operate at a frequency above about 290 MHz or moreand typically between 300 MHz and 400 MHz so that it may be able tooperate for a high speed image processing operation at a rate of 66million polygons per second. The memory modules 3, 3 operate as mainmemory of the CPU module 2, each having a memory capacity of 128 Mbytes.The memory modules 3, 3 are adapted to high speed serial datatransmission between the CPU module 2 and themselves and typicallycomprises so many RDRAMs (Direct Rambus Dynamic Random-access Memories:trademark, available from Rambus Technology).

The printed-wiring board 1 carrying the CPU module 2 and the memorymodules 3, 3 further comprises data transmission wire patterns 4, 5operating as data transmission paths between the CPU module 2 and thememory modules 3, 3 and arranged respectively in the inner layers of thesecond layer and the fourth layer as shown in FIG. 2. The datatransmission wire patterns 4, 5 are designed to show a transmissionfrequency equal to or slightly higher than the operating frequency ofthe CPU module 2 so that they may effectively operate for high speeddata transmissions between the CPU module 2 and the memory modules 3, 3.More specifically, the data transmission wire patterns 4, 5 are designedto show a transmission frequency of about 400 MHz so as to correspond tothe operating frequency between 300 MHz and 400 MHz of the CPU module 2.

The data transmission wire patterns 4, 5 are additionally designed toshow an impedance with a permissible error range specified for the CPUmodule 2 and the memory modules 3, 3 so that the CPU module 2 and thememory modules 3, 3 may accurately identify signals and electric poweris less consumed in a high speed data transmission. More specifically,the data transmission wire patterns 4, 5 are designed to show animpedance of 40±4Ω same as the one specified for the CPU module 2 andthe memory modules 3, 3 including the permissible error range.

The layered structure of the above described embodiment of multilayertype printed-wiring board 1 will be discussed below. Referring now toFIG. 2, the multilayer type printed-wiring board 1 comprises first andsecond inner layer substrates 6, 7. Of these, the inner layer substrate6 carries on one of the surfaces thereof the data transmission wirepattern 4 of the second layer and on the other surface thereof a wiringpattern 8 that operates as a GND layer and forms the third layer. On theother hand, the inner layer substrate 7 carries on one of the surfacesthereof the data transmission wire pattern 5 of the fourth layer and onthe other surface thereof a wiring pattern 9 that operates as a powersupply layer and forms the fifth layer. Then, the inner layer substrates6, 7 carrying thereon respectively the wiring pattern 8 of the thirdlayer and the data transmission wire pattern 5 of the fourth layer thatare arranged vis-a-vis are pressed and bonded together with a prepreglayer 10 interposed therebetween, said prepreg layer 10 being made ofglass fibers impregnated with epoxy resin.

Another wiring pattern 12 that operates as a GND layer and forms thefirst layer is arranged on the inner layer substrate 6 with anotherprepreg layer 11 interposed therebetween. Still another wiring pattern14 that operates as a signal layer and forms the sixth layer is arrangedon the inner layer substrate 7 with still another prepreg layer 13interposed therebetween. Thus, the multilayer printed-wiring board 1having the above listed layers shows a strip line structure, in whichthe data transmission wire pattern 4 is sandwiched by the inner layersubstrate 6 that operates as an insulating layer and the prepreg layer11 and the insulating layer is provided on the opposite surfaces thereofwith the respective wiring patterns 8, 12, whereas the data transmissionwire pattern 5 is sandwiched by the inner layer substrate 7 thatoperates as an insulating layer and the prepreg layer 10 and theinsulating layer is provided on the opposite surfaces thereof with therespective wiring patterns 8, 9.

Meanwhile, the above described data transmission wire pattern 4, 5 arerequired to show an impedance equal to 40±4Ω in order for each of theCPU modules 2 and the memory modules 3, 3 to accurately recognizesignals and realize a high speed data transmission therebetween. Forthis purpose the multilayer type printed-wiring board 1 is provided withchecking coupons 16, 17 for checking the respective impedances of thedata transmission wire patterns 4, 5. More specifically, the impedancemeasuring wire patterns of the checking coupons 16, 17 are arranged inthe respective layers of the data transmission wire patterns 4, 5 andthe impedances of the impedance measuring wire patterns are observed bya TDR unit. To be more accurate, each of the checking coupons 16, 17occupies two separates positions in order to accurately check theimpedance of the data transmission wire pattern 16 or 17, whicheverappropriate. Since both the checking coupons 16, 17 have a sameconfiguration, only the checking coupon 16 will be described below.

Referring to FIG. 3, the checking coupon 16 comprises a first impedancemeasuring wire pattern 21 for measuring the impedance on one of theopposite surfaces of the inner layer substrate 6 that operates as aninsulating layer, a second impedance measuring wire pattern 22 formeasuring the impedance on one of the opposite surfaces of the innerlayer substrate 7 that operates as an insulating layer and land sectionsincluding land sections 23, 23 for signals and a GND land section 24arranged on the prepreg 11 operating as an insulating layer.

The first impedance measuring wire pattern 21 arranged on one of theopposite surfaces of the inner layer substrate 6 is found in the secondlayer same as the data transmission wire pattern 4 and made to show apattern width and a pattern height same as those of the datatransmission wire pattern 4 so that its impedance characteristics may beidentical with those of the data transmission wire pattern 4. The firstimpedance measuring wire pattern 21 is provided at an end thereof with afirst connecting section 21 a for establishing electric connection withone of the land sections 23, 23 for signals that is brought into contactwith the probe arranged in the first layer and at the other end thereofwith a second connecting section 21 b for establishing electricconnection with the second impedance measuring wire pattern 22. Thefirst impedance measuring wire pattern 21 is also provided with aperipheral clearance 26 for preventing any electric interference of thewiring pattern 25 arranged adjacently relative to it. The clearance 26has a width more than twice, preferably more than three times, of thewidth W1 of the first impedance measuring wire pattern 21 in order toreliably eliminate any interference of the wiring pattern 25. In thisembodiment, the wiring pattern 25 operates as GND (ground). The firstimpedance measuring wire pattern 21 is formed in the step of patterningthe copper foil bonded onto the inner layer substrate 6 of the secondlayer.

On the other hand, the second impedance measuring wire pattern 22arranged on one of the opposite surfaces of the inner layer substrate 7is found in the fourth layer same as the data transmission wire pattern5 and made to show a pattern width and a pattern height same as those ofthe data transmission wire pattern 5 so that its impedancecharacteristics may be identical with those of the data transmissionwire pattern 5. The second impedance measuring wire pattern 22 isprovided at an end thereof with a first connecting section 22 a forestablishing electric connection with the second connecting section 21 bof the first impedance measuring wire pattern 21 arranged in the secondlayer and at the other end thereof with a second connecting section 22 bfor establishing electric connection with the other land section 23 forsignals arranged in the first layer. The second impedance measuring wirepattern 22 is also provided with a peripheral clearance 28 forpreventing any electric interference of the wiring pattern 27 arrangedadjacently relative to it. The clearance 28 has a width more than twice,preferably more than three times, of the width W2 of the secondimpedance measuring wire pattern 22 in order to reliably eliminate anyinterference of the wiring pattern 27. In this embodiment, the wiringpattern 27 operates as GND (ground). The first impedance measuring wirepattern 22 is formed in the step of patterning the copper foil bondedonto the inner layer substrate 7 of the fourth layer.

The prepreg layer 11 is formed on the first impedance measuring wirepattern 21 arranged on one of the surfaces of the inner layer substrate6 and the land section 23 for signals to be brought into contact withthe probe of the TDR unit for measuring impedances and the GND landsection 24 are arranged in part of the wiring pattern 12 of the GNDlayer that is by turn arranged on the prepreg layer 11. The landsections 23, 23 for signals are made to show a substantially circularprofile and the GND land 24 is arranged around the outer peripheries ofthe land sections 23, 23 for signals with the clearances 29 separatingthem from each other in order to electrically isolate it from the landsections 23, 23 for signals as part of the wiring pattern 12 arrangedaround the prepreg layer 11 and operating as GND.

Now, the electric connections between the land sections 23, 23 and 24 ofthe first layer, the first impedance measuring wire pattern 21 of thesecond layer and the second impedance measuring wire pattern 22 of thefourth layer will be described below. The first impedance measuring wirepattern 21 and the second impedance measuring wire pattern 22 areelectrically connected to each other by way of the second connectingsection 21 b of the second impedance measuring wire pattern and thefirst connecting section 22 a of the second impedance measuring wirepattern 22 illustrated in FIGS. 2 and 3. As shown in FIGS. 2 and 3, thesecond connecting section 21 b of the second impedance measuring wirepattern 21 and the first connecting section 22 a of the second impedancemeasuring wire pattern 22 are electrically connected to each other bybonding the inner layer substrates 6, 7 with the prepreg layer 6interposed therebetween, subsequently boring a through hole 31 runningthrough the second connecting section 21 b and first connecting section22 a by means of a drill and forming a plating layer (not shown) on theinner wall of the through hole by means of a non-electrolytic orelectrolytic plating method.

One of the land sections 23, 23 for signals of the first layer iselectrically connected to the first connecting section 22 a of the firstimpedance measuring wire pattern 21 of the second layer. On the otherband, the other land section 23 for signals and the first connectingsection 22 a are electrically connected to each other by boring athrough hole 32 through the center of the land section 23 for signals ofthe substrate integrally that is formed by laying the prepreg layer 11where the copper foil of the first layer is bonded to the inner layersubstrates 6, 7 that are bonded to each other on the prepreg layer 13where the copper foil of the sixth layer is bonded and bonding the twoprepreg layers together in a press process and subsequently forming aplating layer on the inner wall of the through hole 32.

The other land section 23 of the first layer is electrically connectedto the second connecting section 22 b of the second impedance measuringwire pattern 22 of the fourth layer. To be more accurate, the other landsection 23 for signals and the second connecting section 22 b becomeelectrically connected to each other by forming a plating layer (notshown on the inner wall of a through hole 33 that is formedsimultaneously with the above described through hole 32.

Meanwhile, the first and second impedance measuring wire patterns 21, 22are made to have a length L that is not less than about 30 mm in orderto ensure that the impedance measured by means of a TDR unit shows astable waveform.

In the case of this embodiment, the applicable transmission frequency ofthe first and second impedance measuring wire pattern 21, 22 arrangedrespectively in the layers of the data transmission wire patterns 4, 5is 400 MHz. Therefore, if a digital signal of 400 MHz is transmitted asa base band signal, the use of a band of 1.2 GHz is required.Since  the  effective  wavelength  λ    is    expressed  by    formula  C  0  (light    velocity  in    vacuum) = λ  0(wavelength) × f(frequency), λ  0 = C  0/f = (3 × 108)/(1.2 × 107) = 2.5 × 10⁻¹ = 0.25(m) = 250(mm)is obtained.

Therefore, the effective wavelength λ in a conductor is expressed by[Formula 1] below.${\lambda\left( {{effective}\quad{wavelength}} \right)} = {{\lambda_{0}/\sqrt{ɛ\quad{{eff}\left( {{coefficient}\quad{of}\quad{self}\text{-}{induction}} \right)}}} = {{0.25/\sqrt{4}} = {{0.125(m)} = {125{mm}}}}}$

When measuring impedances by means of a TDR unit, the minimal length, ormin L, of the data transmission wire patterns 4, 5 is expressed byformula below.min L=λ/4=0.125/4=0.03125 (m)≈30 (mm)  [Formula 1]

Note that min L is made equal to a quarter of the effective wavelength,or λ/4, because it is the minimum length necessary for reproducing theoriginal waveform, taking the influence of reflections and other factorsdue to mismatched impedances into consideration.

In other words, the data transmission wire patterns 4, 5 are required tohave a minimal length expressed by formula below in order to measure theimpedances thereof by means of a TDR unit.min L≧(applicable transmission frequency×3)/4

In this embodiment, a length of 65 mm is selected because it representsthe most table value as shown in Table 1 below. TABLE 1 pattern length L(mm) less than 30 30 50 55 60 65 70 90 100 or more measured unmeasurable52.1 51.5 51.3 51.1 51.1 51.1 51.1 51.1 value (Ω)

Meanwhile, as shown in FIGS. 4A and 4B, the wiring pattern 12 thatoperates as part of the checking pattern 16, the wiring pattern 25 ofthe second layer and the wiring pattern 27 of the fourth layer areelectrically connected to each other by way of the plating layer (notshown) on the inner surfaces of the plurality of through holes 34 so asto eliminate any inductance component of the wiring patterns 25, 27. Thethrough holes 34 are arranged at a pitch as defined below.gap P (mm)≦(propagation velocity)÷(4×thrice of applicable frequency)≦(wavelength at 1.2 GHz in copper)/4≦125 (mm)/4≦31.25 (mm)

The above described checking patterns 16, 17 are used to measure theimpedances of the data transmission wire patterns 16, 17 of themultilayer type printed-wiring board 1. A TDR (time domainreflectometer) unit is typically used to observe the impedances. Asshown in FIG. 5, a TDR unit comprises a probe 40 that is provided withsignal terminals 41, 41 to be held in contact with the respective landsections 23, 23 for signals, to which a voltage is applied, and a GNDterminal 42 to be held in contact with the GND land section 24. From theviewpoint of the checking patterns 16, 17, the signal terminals 41 arebrought into contact with the respective land sections 23, 23 forsignals and the GND terminal 42 is brought into contact with the GNDland section 24 when measuring the impedances. The TDR unit is used tomeasure the impedances of the first and second impedance measuringpatterns 21, 22 by determining the ratio of the voltage of the incidentwave to that of the reflected wave as shown in FIG. 6.

Referring to FIG. 3, since the first impedance measuring pattern 21 andthe second impedance measuring pattern 22 of the multilayer typeprinted-wiring board 1 are electrically connected to each other, it ispossible to measure both the impedance of the first impedance measuringpattern 21 arranged in the second layer and that of the second impedancemeasuring pattern 22 arranged in the fourth layer in a single measuringsession. In other words, the TDR unit can measure both the impedance ofthe first impedance measuring pattern 21 and that of the secondimpedance measuring pattern 22 by counting the elapsed time since thestart of the measuring session.

Referring to FIG. 6 showing the waveform displayed on the monitoringscreen of the TDR unit, the observed impedance fluctuates at point Athat corresponds to the land sections 23, 23 and then fluctuates againat point B that corresponds to the second connecting section 21 a andthe first connecting section 22 a connecting the first impedancemeasuring pattern 21 and the second impedance measuring pattern 22.Thereafter, the observed impedance fluctuates once again at point C thatcorresponds to the second connecting section 22 b of the secondimpedance measuring pattern 22. The observed impedance is held to aconstant level both in the interim between point A and point B and inthe interim between point B and point C. Therefore, when the impedanceis visually observed, it is possible to check the impedance of the firstimpedance measuring pattern 21 and that of the second impedancemeasuring pattern 22 by locating point A, point B and point C where theimpedance fluctuates in the waveform of impedance.

With the above described multilayer type printed-wiring board 1, theimpedances of the data transmission wire patterns 4, 5 can be controlledin a simple manner because the first impedance measuring pattern 21 andthe second impedance measuring pattern 22 having a width and a heightsame as those of the data transmission wire patterns 4, 5 that arearranged in inner layers are located respectively in the layers same asthose of the data transmission wire patterns 4, 5. Additionally, asshown in FIG. 3, the impedances of the wiring patterns arranged indifferent layers can be measured in a single measuring session toremarkably reduce the time required for the checking process because thefirst impedance measuring pattern 21 and the second impedance measuringpattern 22 are electrically connected to each other by way of the secondconnecting section 21 b and the first connecting section 22 a.

While the present invention is described above in terms of a six-layeredprinted-wiring board 1, the present invention is by no means limitedthereto and may also be applied to a printed-wiring board as shown inFIG. 7.

Referring to FIG. 7, the printed-wiring board 50 comprises twoelectro-conductive layers and a first wiring pattern 52 operating as aGND layer is arranged on one of the surfaces of substrate 51 while asecond wiring pattern 53 operating as a signal layer is arranged on theother surface of the substrate 51. With a printed-wiring board 50 havingsuch a configuration, it may be so arranged that land sections forsignals and a GND land section are provided at the side of the firstwiring pattern 53 and a measuring probe is provided at the side of thesecond wiring pattern 52.

1. A multilayer type printed-wiring board comprising; a first insulatinglayer; a data transmission wire pattern arranged on said firstinsulating layer and adapted to data transmission between a CPU moduleand a main memory module to be used for the CPU; an impedance measuringwire pattern arranged on said first insulating layer in the layer sameas that of said data transmission wire pattern with a predeterminedclearance to any adjacent wiring pattern; a second insulating layerarranged on said data transmission wire pattern and said impedancemeasuring wire pattern; and land sections for signals arranged on saidsecond insulating layer and electrically connected to said impedancemeasuring wire pattern arranged on said first insulating layer by way ofa through hole so as to be held in contact with the signal terminal ofthe probe for measuring the impedance of said impedance measuring wirepattern and a GND (grounding) land section held in contact with the GNDterminal of said probe; said impedance measuring wire pattern having apattern length not smaller than about 30 mm and a pattern width same asthat of said data transmission wire pattern.
 2. The multilayer typeprinted-wiring board according to claim 1, wherein the transmissionfrequency of said data transmission wire pattern is not less than 130MHz.
 3. The multilayer type printed-wiring board according to claim 1,wherein the clearance between said impedance measuring wire pattern andany adjacent wiring pattern is not less than twice of the pattern widthof said impedance measuring wire pattern.
 4. The multilayer typeprinted-wiring board according to claim 1, wherein the wiring patternarranged around the impedance measuring wire pattern is a GND patternconnected to said GND land section by way of a plurality of throughholes.
 5. The multilayer type printed-wiring board according to claim 1,wherein a plurality of impedance measuring wire patterns are arranged indifferent layers and electrically connected to each other by way ofthrough holes.
 6. A method of measuring the impedance of a multilayertype printed-wiring board comprising: a first insulating layer; a datatransmission wire pattern arranged on said first insulating layer andadapted to data transmission between a CPU module and a main memorymodule to be used for the CPU; an impedance measuring wire patternarranged on said first insulating layer in the layer same as that ofsaid data transmission wire pattern with a predetermined clearance toany adjacent wiring pattern; a second insulating layer arranged on saiddata transmission wire pattern and said impedance measuring wirepattern; land sections for signals arranged on said second insulatinglayer and electrically connected to said impedance measuring wirepattern arranged on said first insulating layer by way of a through holeso as to be held in contact with the signal terminal of the probe formeasuring the impedance of said impedance measuring wire pattern and aGND (grounding) land section held in contact with the GND terminal ofsaid probe; and said impedance measuring wire pattern having a patternlength not smaller than about 30 mm and a pattern width same as that ofsaid data transmission wire pattern; said method comprising a step of:measuring the impedance of said impedance measuring wire pattern bybringing the signal terminal and the GND terminal of said probe intocontact respectively with said land sections for signal and said GNDland section.
 7. The method of measuring the impedance of a multilayertype printed-wiring board according to claim 6, wherein the transmissionfrequency of said data transmission wire pattern is not less than 130MHz.
 8. The method of measuring the impedance of a multilayer typeprinted-wiring board according to claim 6, wherein the clearance betweensaid impedance measuring wire pattern and any adjacent wiring pattern isnot less than twice of the pattern width of said impedance measuringwire pattern.
 9. The method of measuring the impedance of a multilayertype printed-wiring board according to claim 6, wherein the wiringpattern arranged around the impedance measuring wire pattern is a GNDpattern connected to said GND land section by way of a plurality ofthrough holes.
 10. The method of measuring the impedance of a multilayertype printed-wiring board according to claim 6, wherein a plurality ofimpedance measuring wire patterns are arranged in different layers andelectrically connected to each other by way of through holes.
 11. Themethod of measuring the impedance of a multilayer type printed-wiringboard according to claim 10, wherein the impedances of said wiringpatterns arranged in different layers are measured by measuring saidplurality of impedance measuring patterns arranged in different layersin a single measuring operation.